Variables in Python

Variables serve as containers for storing data values. In Python, they are created the moment you assign a value to them. A variable consists of three key elements: a descriptive name, an assignment operator, and a value.

Naming Conventions

• Variable names must start with a letter or underscore, never a number
• Names can only contain alphanumeric characters and underscores
• Reserved keywords cannot be used as variable names
• Names should be meaningful and describe the data they hold

Comments

Python supports single-line comments using the # symbol and multi-line comments using triple quotes.

# This is a single-line comment

'''
This is a multi-line comment
spanning multiple lines
'''

"""
Another way to write
multi-line comments
"""

Data Types

Numeric Types

Integers

Integers are whole numbers without decimal points. They support standard arithmetic operations.

user_id = 1001
phone_number = int(13800138000)

# Arithmetic operations
num_a = 15
num_b = 4

print(num_a + num_b)   # Addition: 19
print(num_a - num_b)   # Subtraction: 11
print(num_a * num_b)   # Multiplication: 60
print(num_a / num_b)   # Division: 3.75
print(num_a % num_b)   # Modulus: 3
print(num_a // num_b)  # Floor division: 3
print(num_a ** num_b)  # Exponentiation: 50625

Floats

Floating-point numbers represent decimal values.

monthly_salary = 15000.50
height_meters = float(180)  # Converts to 180.0

# Mathematical operations
import math
result = math.sqrt(16)  # 4.0
log_value = math.log(10)  # Natural logarithm

String Type

Strings are sequences of characters enclosed in single, double, or triple quotes.

first_name = 'John'
last_name = "Doe"
address = '''
123 Main Street,
New York, NY 10001
'''

# String methods
text = "Hello World"
print(text.startswith("Hello"))  # True
print(text.endswith("World"))    # True

# Indexing and slicing
message = "Python Programming"
print(message[0])      # P (first character)
print(message[-1])      # g (last character)
print(message[0:6])     # Python
print(message[::2])     # Pto rgamn (step of 2)

String Operations: join() and split()

# Join - combines list elements into a string
char_list = ['P', 'y', 't', 'h', 'o', 'n']
joined_string = '-'.join(char_list)
print(joined_string)  # P-y-t-h-o-n

# Split - breaks string into list
sentence = "apple,banana,cherry"
fruits = sentence.split(',')
print(fruits)  # ['apple', 'banana', 'cherry']

List Type

Lists are ordered, mutable collections that can hold multiple data types.

# Creating lists
hobbies = ['reading', 'gaming', 'coding']
empty_list = []
converted_list = list('abc')  # ['a', 'b', 'c']

# Accessing elements
print(hobbies[0])    # reading
print(hobbies[-1])   # coding
print(hobbies[1:3])  # ['gaming', 'coding']

# Modifying lists
hobbies.append('music')
hobbies.remove('gaming')

Dictionary Type

Dictionaries store data in key-value pairs, providing fast lookups by key.

# Creating a dictionary
person_info = {
    'name': 'Alice',
    'age': 28,
    'city': 'Beijing',
    'skills': ['Python', 'Java', 'SQL']
}

# Accessing values by key
print(person_info['name'])       # Alice
print(person_info.get('age'))    # 28

# Modifying values
person_info['age'] = 29
person_info['email'] = 'alice@example.com'  # Add new key

# Deleting a key-value pair
del person_info['city']

Configuring Pip Mirror Sources

When installing Python packages, the default pip source may be slow due to geographic distance. Configuring a domestic mirror significantly improves download speeds.

Common Chinese mirror sources include:

• Tsinghua: https://pypi.tuna.tsinghua.edu.cn/simple
• Aliyun: https://mirrors.aliyun.com/pypi/simple
• Douban: https://pypi.douban.com/simple

To permanently configure a mirror, modify the pip configuration file or use the command:

pip config set global.index-url https://pypi.tuna.tsinghua.edu.cn/simple

Jieba Library for Chinese Word Segmentation

Jieba is a powerful Chinese text segmentation library. Install it using pip:

pip install jieba

Segmentation Methods

import jieba

text = "Artificial intelligence is changing the world"

# Accurate mode (default) - returns list
seg_result = jieba.lcut(text)
print(seg_result)
# ['Artificial', 'intelligence', 'is', 'changing', 'the', 'world']

# Full mode - scans all possible words
full_seg = jieba.lcut(text, cut_all=True)
print(full_seg)

# Search engine mode - better for search indexing
search_seg = jieba.lcut_for_search(text)
print(search_seg)

# Adding custom words
jieba.add_word("Artificial intelligence")
custom_seg = jieba.lcut("Artificial intelligence is developing rapidly")
print(custom_seg)

Generating Word Clouds with wordcloud

The wordcloud library creates visual representations of text data. Install required packages:

pip install wordcloud
pip install imageio
pip install pillow

Basic Word Cloud Generation

import jieba
import wordcloud

# Sample text
content = "Python is a powerful programming language used for web development, data analysis, machine learning, and automation. Python has a simple syntax and is easy to learn."

# Segment Chinese text (for Chinese content)
words = jieba.lcut(content)
text_processed = ' '.join(words)

# Create word cloud
wc = wordcloud.WordCloud(
    width=800,
    height=400,
    background_color='white'
)

wc.generate(text_processed)
wc.to_file('wordcloud_output.png')

Customized Word Cloud with Mask

Using a mask allows you to shape the word cloud into custom forms.

import jieba
import wordcloud
from imageio import imread

# Load mask image (white background required)
mask_image = imread('star_shape.png')

# Text content
sample_text = "Technology innovation drives progress and creates opportunities for development and growth"

# Add custom vocabulary
jieba.add_word("Technology innovation")

# Process text
word_list = jieba.lcut(sample_text)
processed_text = ' '.join(word_list)

# Configure word cloud with mask
cloud = wordcloud.WordCloud(
    font_path='C:/Windows/Fonts/simhei.ttf',  # Chinese font support
    mask=mask_image,
    background_color='white',
    width=1000,
    height=800,
    max_words=100
)

cloud.generate(processed_text)
cloud.to_file('custom_shaped_wordcloud.png')

Key parameters for WordCloud customization:

• font_path: Path to font file for Chinese character support
• mask: Image array defining the shape
• background_color: Background color (default: black)
• max_words: Maximum number of words to display
• width, height: Output image dimensions
• colormap: Color scheme for words